GitLab

Convert hadrian buildscripts to unsuffixed, dashed form

final cleanups

This exposes the flag of the same name supported by the testsuite
driver.

I've ruined two trees already by failing to pass --flavour to hadrian.
Let's factor this out so it can be reused during troubleshooting.

Darwin sh doesn't support \e.

Previously our attempt to cache the cabal store would
`cp cabal-cache ~/.cabal`. However, if the latter already
 existed this meant that we would end up with
~/.cabal/cabal-cache. Not only would this not help caching
but it would exponentially grow the size of ~/.cabal. Not
good!

This moves nearly all of the CI logic to .gitlab/ci.sh. This improves
things in a number of ways:

 * it's harder for inconsistencies to arise between architectures
 * it's easier to share logic between architectures
 * on Windows, it's easier to ensure that all CI steps are executed from
   within a properly initialized mingw session.

While in town I also add a FreeBSD build job and update the Windows job
to use the gitlab-runner PowerShell executor, since cmd.exe will be
deprecated soon (fixing #17699).